Naturally-occurring poly(.beta.-hydroxyalkanoates) are a class of biodegradable polymers which have been the subject of increasing interest as a material which can be employed in disposable articles and specialty medical products. Generally, these polymers exhibit biologically-mediated environmental degradability, hydrolytic degradation and have been shown to possess advantageous characteristics when used in vivo. The most well-known of the poly(.beta.-hydroxyalkanoates) are homopolymers of poly(.beta.-hydroxybutyrate) and copolymers of .beta.-hydroxybutyrate and .beta.-hydroxyvalerate. See, for example, Brandl et al., Adv. in Biochem. Eng./Biotech., 41:77 (1990); Doi, Y., Microb. Polyesters, VCH Publishers: New York (1990); Steinbuchel et al., Mole. Microb., 5(3):535 (1991).
Polyesters have been formed by the ring-opening polymerization of lactones and lactides which show biodegradability and biocompatibility. Further, application of specific linear polyesters, such as poly-.epsilon.-caprolactone and polylactides, in medical technology has been the subject of particular recent attention. For example, polylactides exhibit relatively rapid bioerodability. In addition, copolymers and diblock copolymers have recently been formed of polylactide and polycaprolactone. See, for example, Jacobs et al., Macromolecules, 24(11):3027-3034 (1991) and Dubois et al., Macromolecules, 24(9):2266-2270 (1990).
However, the physical properties of poly(.beta.-hydroxyalkanoates) and of linear polyesters formed of lactides and lactones are typically distinct. Consequently, the versatility of articles formed from polymers which include only .beta.-hydroxyalkanoates or biodegradable linear polyesters, such as lactides and lactones, is limited.
Therefore, a need exists for biodegradable and hydrodegradable polymers and methods of forming such polymers which overcome the aforementioned problems.